In conventional serial transmission of digitized real-time video data signals, a typical communications channel has insufficient capacity to carry the large amount of data needed to accurately represent a moving video picture. For example, in a typical video system operating at 30 frames per second, where each frame has a resolution of 720×480 picture elements (pixels) with each pixel requiring 8 descriptive data bits, a transmission channel having a capacity of 83 M bits per second would be required. Such high data rates far exceed the practical transmission systems in use today.
Thus, various data reduction techniques are typically employed to reduce a real-time data transmission to more a manageable size. Such techniques typically reduce or inhibit the transmission of pixel data that is unchanged from a predecessor frame. While this works well for predominately static images, images that contain complex motion require a more sophisticated mathematical modeling of the video motion.
Typically, such modeling features a comparison and analysis of groups of pixels to detect changes that occur between successive video frames. Once such motion is identified, x-y directional translation vectors can be determined that are used for a predictive estimation of a motion field. To reduce the resulting vector data to conform to the communication channel, however, requires that the size of the pixel group be rather large, such as that of conventional widely used video encoding standards, which compare an 8×8 or a 16×16 pixel area or block. As can be seen, such “block-based” motion encoding significantly lowers the amount of data to be transmitted.
However, a significant drawback of such systems is any motion is assumed to be constant over the entire block. Thus, this relatively large size of the fixed comparison block leads to an objectionable visual distortion in the received picture when motion fields are rapid. This is perceived as a tiling effect and effectively reduces image resolution via the associated 8- or 16-bit motion step.
A further drawback is that any changes at individual pixels sites are effectively averaged with the entire block, and any complex motion that is contained within a pixel area smaller than the selected comparison block size is generally not detected. Such small motion is therefore not included in the transmission, nor the subsequent display of the image at the receiving entity, giving attendant degradation in viewing resolution.